A method of separating gaseous isotope mixtures by exciting the rotational vibration levels utilizing narrow-band electromagnetic radiation with subsequent separation of the non-excited isotopes by physical or chemical means has already been disclosed in German patent document Auslegeschrift No. 1,296,611. However, here the excitatory radiation for the isotope mixture undergoing separation must be accompanied by additional electromagnetic radiation of wavelength and bandwidth such that the excited isotope molecules become ionized.
Another method of separating isotopes, in particular U.sup.235 and U.sup.238, by means of laser radiation, has been disclosed in German patent document DOS No. 1,959,767. Here, however, it is necessary, before injecting the laser light, to raise the reaction mixture to a predetermined temperature, which must be of such level that perceptible reaction just ceases to take place.